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Ok so I signed up last week on thumper talk because I had a bad issue with my bike smoking and fouling plugs. The solution was a new head gasket as my old one was leaking h2o into the cylinder. That solved the problem of clouds coming from my exhaust. I'm still having the fouling problem. If I idle too long (30s), and then give some throttle it goes wwwaaaaaa pop pop wwaaaaaa bluuuhhrrrrrrr...dead(fouled plug). Basically it blubbers and blurrs until it dies. Just yesterday I noticed that if I just barely give it enough throttle to stay on 2 wheels it'll clear up after about a minute then I can rip and run. I've already downsized my pilot jet one size from stock. And from what I learned, it seems like maybe my needle is too high?? What do you guys diagnose this as?


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Welcome to the forums!

What make, model, year bike ?

 

If it ever ran fine before on the same jetting specs, then jetting isn't the problem.

 

Low compression, worn components (rings, reeds, saturated silencer packing) will all make the engine 'act' rich.

A worn / damaged right hand side crank seal will allow gearbox oil into the crankcase, also creating a rich condition.

Using a high flash point 'racing' premix will make things worse if the engine is not in tune.

A too high fuel / float level in the carburetor will richen each fuel metering circuit. 

 

Cleaning and re-using plugs you've fouled before will make them even more prone to fouling again. 

 

Jetting is the last thing to fine tune after you've confirmed the rest of the engine is mechanically sounds (in-specs).

Edited by mlatour
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2005 cr125
It was a fouler since it came out of the crate, but as a recall, me and my dad fixed the issue years ago. Someone stole the bike and I changed the crank bearings, seals, top end, carb kit, etc.
The compression is at 132psi. The reeds seem to be in decent condition. The float height is as close as I could measure. During these years, the packing did get saturated (I know it's not proper but I took the packing out and flushed it with gasoline to clean out the black goop). Would packing make it rich at a certain throttle point? The plugs are wet and black when I pull them. Also I'm running the Honda 2 stroke oil.

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132psi sounds quite low, (holding the throttle wide open as you crank?)

How many hours on it since the rebuild?

 

Reed damage can be judged by looking, but not wear/fatigue. They are a wear item just like a piston & ring.

 

Gearbox oil level been dropping lately?

 

 

Edited by mlatour

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Yea I checked compression properly. I'm not really sure about the hours. The bike sat for at least a year before I started working on it. I took the reed cage off and shined a light through. All i could see was a sliver of light, maybe 0.001". The gear oil level was actually high so we can likely rule out crank seals.

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No 125 is designed to idle for more than a few seconds. Even if the jetting is close to perfect you will have a little issue. And as the temps get warmer you may need to go smaller on the pj. What is your air screw setting? That might clear it up.

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No 125 is designed to idle for more than a few seconds. Even if the jetting is close to perfect you will have a little issue. And as the temps get warmer you may need to go smaller on the pj. What is your air screw setting? That might clear it up.

My air screw is like 2.5 turns out. I just realize that if I move my throttle cable on the carb it revs a little also.
Should I go down another size on the pilot. It's like 90-95° here
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It shouldn't hurt going down a pilot size if you are at 2.5 turns out...
You shouldn't see any light through the reeds...
Moving your throttle cable should not increase revs...sounds like your cable should be adjusted...
Gotta fix all the little stuff to get it jetted and running well...

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Right main crank seal. Mine somehow backed out and was running the same. When it cleaned out it would run lean, like throttle stuck I think it was sucking air through the crankcase vent.

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Okay guys they manual reccomended a 55 pilot. I've had to go to a 45 to get the bike to idle up while turning the air screw. Still it fouls after putting around for about 30 sec. Please don't tell me they aren't supposed to run slow...i have a cr250r that can idle around all day without fouling a single plug. I'm gonna go broke fouling spark plugs with this darn thing. Anyone wanna trade for a crf250?

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53 minutes ago, Sofiedog said:

It could be a lot of things...did you say your needle clip was in the middle? Raising the clip drops the needle and helps lean out the 1/8 - 1/2 throttle positions.

It will actually affect 1/8 - 3/4 throttle positions.

http://www.iwt.com.au/mikunicarb.htm

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have you tried since you replaced the head gasket?

Yes. Is it possible I need to change the needle jet and not the needle? That's the only thing not tinkered in my carb

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The Mikuni carb that came on the newer gen 02-07 CR's was well known as having very rich factory jetting specs.   

What position is the needle clip at ?

132 psi sounds low for a 125cc 2T. What gauge did you use to take the comp. test ?  If it's a harbor freight or a generic one it could be giving you a wrong reading since you stated it has a recent topend done.

Edited by H4L

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On 6/22/2017 at 5:26 PM, whattohunt said:

Okay guys they manual reccomended a 55 pilot. I've had to go to a 45 to get the bike to idle up while turning the air screw. Still it fouls after putting around for about 30 sec. Please don't tell me they aren't supposed to run slow...i have a cr250r that can idle around all day without fouling a single plug. I'm gonna go broke fouling spark plugs with this darn thing. Anyone wanna trade for a crf250?

Put your fouled plug in white vinegar for a day or two and it will be good as new. Put a little anti-sieze on the threads. A fouled plug is just dirty, nothing wrong with it. 

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Put your fouled plug in white vinegar for a day or two and it will be good as new. Put a little anti-sieze on the threads. A fouled plug is just dirty, nothing wrong with it. 

Just tried it. Works great. I took a used plug that I cleaned my usual way with mineral spirits and a fine steel brush n paper towels. It looked pretty good. I let it soak in white vinegar for a couple hours and more stuff came off/out of the plug just by swirling around.IMG_2066.thumb.JPG.fe4ce6c47264987a3fb4dbf4928b8d77.JPGIMG_2069.thumb.JPG.254713b0aeeebdf9a3f4238ca752cfc3.JPG

Good reminder to put oil or something on the threads afterward.

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